Voice current repeater



InUEl-l DT' Hnwarc H. 5ml-L H. H. SMITH VOICE CURRENT REPEATER Filed Sept. 2, 1930 Qmm si 56.5%:

Nov. 29, 1932.

Patented Nov. 29, 1932 ETE STATES PATENT FFICE HOWARD I-I. SlfIITI-I, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE! ASSIGNMENTS, ASSOCIATED ELECTRIC LABORATORIES, INC., F CHICAGO,v ILLINOIS, A CORPORATION OF DELAVJARE VOICE CURRENT REPEATER Application filed September 2, 1930. Serial No. 479,253.

This invention relates to voice current repeaters in general, but in particular to voice current repeaters of the switching type which v are capableof two-way repetition in long distance telephone lines. `he principal object of this invention, briefly stated, is the provision of a switching type repeater which is eX- ceedingly rapid and reliable in its operation and which is particularly adaptable for operation in telephone circuits in which are included composite telegraph sets for telegraph operation.

One feature oi" the invention is the arrangement whereby heater type tubes may be used inthe repeater without any loss of speech because of the normal time required for tubes of that type to reach the effective operating temperature. f

Other objects and features of the invention will be apparent from the accompanying single sheet of drawing and the following description.

In the drawing, there is diagrammatically depicted by means. of usual circuit symbols,

a voice current repeater constructed iii accoi-dance with thisinvention. This repeater is provided with a transmission path tor each direction or' travel ot the voice vcurrents through the repeater and each transmission "530 path includes what will hereinafter be termed a line amplifier which aiiiplifies and repeats the voice current for conversational purposes.

These line amplifiers are normally condirtioned to receive voice currents inthe proper direction, but are normally prevented from repeating` them until a switching operation takes place to close their normally open output circuits. ciated with it a switching ampliiier, the output of which is used solely to operate a voice current relay to perform the aforementioned switching operations.

In order that the direction of travel ot voice current may readily be seen, that portion of the telephone trunk, or line, which is shown connected to the repeater at the left side of the dra-wing is termed line west, while that at the right is termed line east, Likewise, that line amplilier and that switchv Each line amplifier has ass0-' ing ampliiier tor west-toeeast transmission nected to the heating elements before the operating temperature of the tube is reached.

Thus it can be seen that if such tubes are used in voice current repeaters without being preheated, the result would be the loss of a concording to this invention, this preheating arrangement lias been taken care of by supplying a common battery as the source of A current for all of the tubes of the various `ampliiiers, the current froinwhich battery is supplied to the filaments of the tube through a resistor when the repeater is not infuse, so that the tubes will receive only sufcient current to keep them heated for immediate operation. A low resistance circuit around said resistor and means for closing that circuit when the repeater is taken into use have been provided in order that the filaments may obtain the full voltage for operation. By this arrangement, no time is lost because of cold tubes and the repeaterwill function immediately when taken into service.

vl/'hen the repeater is taken into use,'it is placed in operating condition by the operation of key K which completes the circuit 'of start relay 3. In a manual telephone system, this key K is located at an operators position. The ground supplied to the winding of relay 3 by key K may, as an alternative, be supplied through the sleeve contacts of plug and jack connections to the trunk when it is desired to establish a telephonie connection between two terminating stations. In an automatic telephone system, seizure ot this trunk by an automatic switch will cause the application of ground to the winding of relay 3.

However, regardless of'how the ground is supplied to relay 3, that relay operates when its circuit is completed and at its armature l1 completes the low resistance path about siderable portion of the initial speech. yAci-'65 the resistor R1, in order that the tubes of the amplifier will be supplied with the full voltage output of battery A. It will here be noted that when the repeater is not in use, the filaments of the tubes obtain current from the battery A through the variable resistor R and the fiXed resistor R1 over conductor 10 sufl'icient to keep the filaments heated. The variable resistor R is for the purpose of regulating the supply of operating current to the tubes.

It has been discovered that the heater type vacuum tubes now available commercially will only operate as amplifiers when used as contemplated by this invention if the plate voltage has been greatly increased or, preferably if a positive potential has been placed upon the grid. Accordingly, a battery l) has been shown at each end of the drawing with its positive terminalconnected in the grid circuits of all of the tubes comprising the line and switching amplifiers at the respective ends of the drawing. These batteries D supply the necessary positive potential to the tubes to render them operative.

Further results of the operation of relay 3 are the connection of the plate or space current from battery B to the plates of the vacuum tubes by way of armature 13 and its make contact and conductor 16, and the connection of ground G to the windings of the remainder vof the relays and to the vibrating contacts of relays 5 and 5 by way of armature 12 and its make contact. It will be noted in the drawing that all ground connections supplied from ground G through armature 12 have been represented by encircled ground symbols. This has been done to simplify the drawing in order that the invention might not be obscured by multiplicity of lines leading from the make contact of armature 12 to these various relays.

When ground is so connected by relay 3 through its armature 12, the upper windings of relays 1, 5 and 6 and the lower windings of relays 2, 5 and 6 energize in the obvious circuits, while the middle windings of relay 5 and 5 energize through the normally engaged contacts of relays 4 and t, respectively. Also, the lower winding of relay 6 and the upper winding of relay 2 are energized through the contacts of relay 4;, armature and resting contact of relay 5, thence by way of conductor 7, while the upper winding of relay 6 and the lower winding of relay 1 are energized through the contacts of relay 4, armature and resting contact of relay 5', and thence by way of conductor 7.

Relays 1, 2, 5, 5. 6 and 6 are balanced differential relays, that is, the two windings have equal and opposite effects and thereby neutralize eachother when energized at the same time. Therefore, when the two winding of each of these relays are energized simultaneously, the relays remain inert. The

third windings of relays 5 and 5 are employed to make those relays slow-to-release in the well known manner.

Therefore, with the exception of relay 3,

the connection of ground through the winding of the relay 3 leaves the equipment in the condition in which the parts are shown in the drawing. However, since the amplifiers are now receiving their full supply of A current and since the B current has been connected to the plate and the various relays have been energized, the repeater is in,V condition to repeat voice currents in either direction.

Assuming, now, that voice currents Coirmence to flow in the west-east direction, they will be received by the repeater over line west7 and through the west repeating coil REV. Since relay 1, although both windings are energized, is in the position shown, the voice currents will be induced in the primary winding of transformer T. As can beseen by the drawing, the west-east line amplifier and the west-east switching amplifier are connected in parallel to the secondary winding of the transformer T. Therefore, both of these amplifiers receive voice currents through the transformer T.

Connected in the output circuit of the two switching amplifiers are the voice current relays a and 1i. These relays are sensitive to voice currents to vibrate their contacts in the same manner as the type of relay disclosed in United States Patent No. 1,221,299, issued to C. J. Erickson, on April 3, 1917.

Since relay el is in the output circuit of the west-east7 switching amplifier, it will respond to the voice currents magnified by Y that amplifier by vibrating its contacts to remove ground from the middle winding of relay 5 and from the conductor 7. fis result, relays 5, 6 and 2 are unbalanced and immediately attract their armatures into engagement with their make contacts. The attraction of the armature of relay 2 connects the secondary winding of the output transformer T1 of the westeast line amplifier to the east line repeating coil RE by way of conductors 8 and 9, thereby completing the westeast transmission, or repeating, circuit through the rep-eater. This attraction of the armature of relay 2 also disconnects the input transformer T of the east-west line and switching amplifiers from the east7 line repeating coil RE and the line east in order that the west-east transmission path may be maintained without interruption as long as voice currents flow in that direction.

Relay 5 in attracting its armature out of engagement with its resting contact opens at that point th-e circuit of the lower winding of relay 6 and the upper winding of relay 2 to prevent restoration of these relays until relay 5 restores. Engagement of the armature of relay 5 with its make contact completes the circuit of the third or lower winding of that relay to establish a path for eddy currents to make relay 5 slow-to-release.

Relay 6 in attracting its armature into engagement with its make contact connects ground to conductor l5, thereby lockingvrelays 5 and 6 against chance operation of the vibrating contacts of relay 4.

Because of the slow-to-release feature of relay 5, this relay will remain operated for a short interval after the contacts of relay 4- cease vibrating following the cessation of voice currents in the west-east direction. This interval during which relay 5 remains operated is greater in length than the ordinary pause between words in conversation in order that the relay 5 will remain operated during such pauses, thereby maintaining its armature attracted to prevent the disruption of the west-east transmission circuit through the repeater.

When the vibrating contacts of the voice current relay 4- remain quiet for a period greater in length than the timerequired for relay 5 to restore, relays 6 and 2 restore because of the neutralizing effect of their windings when ground has been reconnected to conductor 7. thereby restoring the original condition of the repeater for reception of voice currents from either direction.

Since the input transformer T is now connected to the east line repeating coil RE. voice currents traveling in the east-west direction will be r-eceived by the east-west7 line and switching amplifiers. Voice current relay 4C will now be operated from the output of the east-west switching amplifier and will vibrate its contacts to control relays 5. 6 and l in the identical manner in which relays 5, 6 and 2 were controlled by the voice current relay 4e. The output amplifier Tl of the east-west line amplifier is now connected by way of conductors 8 and 9 and armature and make Contact of relay l to the west line repeating coil Rl/V and line west, while the input transformer T of the westeast ampliers is disconnected from repeating coil RW so that a one-way transmission or repeater circuit in the direction eastwest is established through the repeater.

It will be noted that the voice current relay 4 is impedance-coupled to the east-west switching amplifier. This coupling consist-s of the retard coil I and the condenser C and comprises what is termed a thump filter which is of such an impedance as to suppress the low telegraphic frequencies. or thump frequencies, and to favor the high voice current frequencies. By this arrangement chance operation of the relay 4 or interference in its operation by telegraphic frequencies is eliminated.

Connection of ground to conductor 14 by relay 6 prevents the chance operation of rey lays 5 and 6 when the east-west transmisvsion kcircuit has been established through the repeater.

The third or upper winding of relayA 5 makes this relay slow-to-release also for the purpose of maintaining the east-west repeater circuit duringordinary pauses in conversation such as those between words.

Throughout the conversation period the repeater will function to first establish a transmission path through it in one direction and then establish another transmission path through it in the opposite direction as long as conversation between the two terminating stations takes place.

When the conversation is terminated, the operatory will release the key K to restore relay 3, this relay thereupon at its armature 13 disconnects the source of B current from the plates of the vacuum tubes and at its armature 12 removes ground from the windings of the relays and the contactsv of the voice current relays so that when the repeater is not in use there will be no unnecessary drain upon the batteries. At its armature l1, the relay 3 removes the shunt from about the resistor R1 so that the current appliedV to the filaments of the vacuum tubes is reduced, but not entirely removed.

Bridged across the input circuits of the line amplifiers are the gain control devices GC 'l and. GC', which are adjustable to obtain the desired amount of gain of the amplifiers.

It will now be appreciated that a two-way voice current repeater of thel switching type may be constructed to use heater type vacuum tubes in such a way that no loss is sustained for the necessary heating of the tubes before the repeater can function. It will also be appreciated that here is a voice current repeater which can be used with any telephone. line without the necessity of providing a balancing network and especially with a telephone line which has composite telegraph sets included therein for telegraphic transmission over the line.

Having thus described this invention, what is considered new and what is desired to have protected by Letters Patent is pointed out in the appended claims.

What is claimed is:

1. In a two-way repeater circuit, the combination of two repeaters, each having an incoming and outgoing section, the outgoing section of each repeater being normally open, the incoming section of each repeater having an amplifying device for magnifying voice currents for conversational purposes, a. second amplifying device for each repeater for magnifying voice currents for switching purposes, a switching relay for each outgoing section, and a voice current relay associated with each of said second amplifying devices and responsive to the voice currents magnified thereby for operating the switching relay of the associated outgoing section to open the. incoming section of the other repeater and to close said associated outgoing section, and means associated With each repeater and controlled by the associated voice current relay for locking the other repeater against chance operation.

2. In a two-Way repeater circuit,.a voice current amplifier for each direction of repetition through said circuit, each 'amplifier having` a normally open output circuit, a circuit closing device for each output circuit, means individual to each amplifier and responsive to an initial voice current in the proper direction to operate the circuit closing;- device of the associated amplifier to close the output circuit thereof, and other means associated With each amplifier and responsive to the operation of the first-mentioned means individual to the associated amplifier to prevent operation of the first-mentioned means individual to the other amplifier While the output circuit of the associated amplifier is closed. J

3. In a two-Way repeater circuit, a current amplifier for each direction of repetition over the circuit having a normally open output circuit a normally balanced differential relay associated with each amplifier and having means for closing the output circuit of the associated amplifier When the relav is unbalanced, a voice current rela-y individual to each amplifier and responsive to voice currents delivered to the associated amplifier to unbalance the differential relav of the associated amplifier to thereby close the output circuit thereof, and a second balanced differential relay associated With each ampliiier and also unbalanced by the voice current relay individual to the associated amplilier responsive to voice currents beingdelivered thereto to prevent unbalancing of the first mentioned differential relay associated with the other amplifier While the output circuit of the associated amplifier is closed.

In Witness whereof, I hereunto subscribe `my name this 28th day of' August, A. D.

HOWARD H. SMITH. 

